7 Iris

7 Iris
Discovery A
Discoverer John Russell Hind
Discovery date August 13, 1847
Alternate
designations
none B
Category Main belt
Orbital elements C D
Epoch July 14, 2004 (JD 2453200.5)
Eccentricity (e) 0.230
Semi-major axis (a) 357.019 Gm (2.387 AU)
Perihelion (q) 274.729 Gm (1.836 AU)
Aphelion (Q) 439.310 Gm (2.937 AU)
Orbital period (P) 1346.628 d (3.69 a)
Mean orbital speed 19.28 km/s
Inclination (i) 5.523°
Longitude of the
ascending node (Ω))
259.766°
Argument of
perihelion (ω)
145.406°
Mean anomaly (M) 135.770°
Physical characteristics
Dimensions 199.8 km
Mass 8.4—1018 kg
Density 2 ? g/cm³
Surface gravity 0.0558 m/s²
Escape velocity 0.1056 km/s
Rotation period 0.2975 d 1
Spectral class S-type asteroid
Absolute magnitude 5.51
Albedo 0.277 2
Mean surface
temperature
~171 K

Size comparison: the first 10 asteroids profiled against Earth's Moon. From left to right, 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta, 5 Astraea, 6 Hebe, 7 Iris, 8 Flora, 9 Metis, and 10 Hygiea. [Source]

It was the seventh asteroid discovered, on August 13, 1847 by J. R. Hind from London, UK. It was Hinds' first asteroid discovery.

Name

Iris was named after the rainbow goddess Iris of Greek mythology, sister of the Harpies and messenger of the gods, especially Hera. Her quality of attendant of Hera was particularly appropriate to the circumstances of discovery, as she was spotted following 3 Juno (Juno is the Roman equivalent of Hera) by less than an hour of right ascension.

According to the OED, the correct adjectival form of the name is Iridian.

Characteristics

Iris was observed occulting a star on May 26, 1995 and later on July 25, 1997. Both observations give a diameter of about 200 km.

The surface of Iris is very bright and is probably a mixture nickel-iron metals and magnesium- and iron-silicates.



Aspects

Stationary, retrograde Opposition Distance to
Earth (AU)
Maximum
brightness (mag)
Stationary, prograde Conjunction to Sun
April 12th, 2005 June 3rd, 2005 1.81674 9.2 July 27th, 2005 January 24th, 2006
October 10th, 2006 November 14th, 2006 0.85211 6.6 December 16th, 2006 August 25th, 2007
February 14th, 2008 April 9th, 2008 1.85457 9.4 May 29th, 2008 November 21st, 2008
May 15th, 2009 July 4th, 2009 1.55566 8.7 August 24th, 2009 March 19th, 2010
December 8th, 2010 January 23rd, 2011 1.16806 7.9 March 6th, 2011 September 28th, 2011
March 11th, 2012 May 4th, 2012 1.92914 9.5 June 26th, 2012 December 16th, 2012
July 1st, 2013 August 16th, 2013 1.16690 7.9 September 28th, 2013 June 16th, 2014
January 12th, 2015 March 6th, 2015 1.56393 8.9 April 21st, 2015 October 24th, 2015
April 7th, 2016 May 29th, 2016 1.84861 9.2 July 22nd, 2016 January 16th, 2017
September 22nd, 2017 October 29th, 2017 0.85325 6.9 November 28th, 2017 August 16th, 2018
February 9th, 2019 April 5th, 2019 1.82359 9.4 May 25th, 2019 November 17th, 2019
May 8th, 2020 June 27th, 2020 1.61521 8.8 August 18th, 2020 March 6th, 2021

Links

Discovery of Iris", MNRAS 7 (1847) 299

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For a complete listing, see: List of asteroids. For pronunciation, see: Pronunciation of asteroid names.

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